Use of amphiphilic polymers or copolymers for surface modification of reactive inorganic fillers

ABSTRACT

Surface-modified fillers are described characterized by the fact that the fillers represent reactive inorganic fillers and the modifying agent represents an amphiphilic aminoplastic-ether polymer or copolymer of the structural type 
                 
 
in which:
         Z denotes the same or different aminoplastic central units based on melamine-formaldehyde or urea-formaldehyde derivatives;   n=10 to 500;   R denotes the group —[O—CH 2 —CH 2 ] m O—S in which m=5 to 500 and   S represents a substituted or unsubstituted alkyl, aryl, alkaryl or aralkyl group.

DESCRIPTION

The invention concerns surface-modified active inorganic fillersmodified with amphiphilic polymers or copolymers, as well as their usein polymers, especially PVC.

PVC can be stabilized by a number of additives (R. Gächter, H. Müller,Carl Hanser Verlag, 3^(rd) edition, 1989, Plastic Additives). Inaddition to ordinary additives, like epoxidized fatty acid esters, zinc,cadmium, lead and/or alkali and/or alkaline earth carboxylates oraluminum carboxylates, phosphites; antioxidants, β-dicarbonyl compounds,plasticizers, lubricants and pigments, fillers are used. Hydroxides,carbonates, silicates, dolomites can be used as fillers and e.g.titanium dioxide and/or zirconium oxide can be used as pigments. Thecomposition can also contain at least one zeolite compound and a layeredcompound, like hydrotalcite. Hydrotalcites are described in EP-A-0 772648 as active fillers with a stabilizing effect in PVC.

German Patent Application 10038147.2 describes amphiphilic graftpolymers or copolymers that contain the same or different base polymerchains, the same or different central units based on amelamine-formaldehyde or urea-formaldehyde derivative, as well as thesame or different polar or nonpolar side chains. These graft polymers orcopolymers can be used, among other things, as adhesion promotersbetween inorganic or organic pigment and/or filler surfaces and organicpolymer matrices. No specific data are present concerning the type ofpigments or fillers.

It was found that active fillers, like hydrotalcite for polymer masses,can be strongly electrostatically charged during grinding and thereforeare difficult to transport or pack into sacks. These fillers also had atendency to agglomerate and adhere to surfaces of the employed equipmentand pipes, which often led to clogging. The task therefore consisted offinishing these fillers antistatically. At the same time, the antistaticagent was not supposed to adversely affect the stabilizing effect ofthese fillers in polymer masses, especially in halogen-containingpolymer masses, like polyvinyl chloride.

Linear aminoplastic-ether copolymers are known from U.S. Pat. Nos.5,627,232, 5,629,373 and 5,914,373 that contain a bifunctional alkyleneoxy group and a skeletal group of an aminoplastic, like glycoluril.

It was found that amphiphilic aminoplastic-ether polymers areparticularly suitable for surface modification of reactive inorganicfillers.

The object of the invention are surface-modified fillers characterizedby the fact that the fillers represent reactive inorganic fillers andthe modifying agent represents an amphiphilic aminoplastic-ether polymeror copolymer of the structural type

in which:

Z denotes the same or different aminoplastic central units based onmelamine-formaldehyde or urea-formaldehyde derivatives;

n=10 to 500;

R denotes the group —[O—CH₂—CH₂]_(m)O—S in which m=5 to 500 and

S represents a substituted or unsubstituted alkyl, aryl, alkaryl oraralkyl group.

The term “aminoplasts” is the term for melamine, urea, benzoguanine andcarbamide ester resins. Resin in this context means that the melamine,urea, benzoguanine or carbamide monomers were polymerized withformaldehyde to form a “resin”.

Reactive inorganic fillers for polymer masses are understood to meaninoroganic fillers that interact in any way with the polymer masses ortheir decomposition products. Specific mechanical and/or physicalproperties of the polymer matrix can be altered with fillers. Since theactive function can be different in nature, a definition is onlypossible in conjunction with the corresponding polymer. Such fillers areflame retardants and reinforcing fillers, for example. In addition,these fillers can react with substances that form during thermal,chemical or radiation-induced decomposition of the polymer masses. Thesubstances include hydrogen halides that form during decomposition ofhalogen-containing polymer masses, like polyvinyl chloride (PVC).

The reactive fillers preferred for use in halogen-containing polymersare double-layer hydroxides with internal crystalline charge balance andcan be described by the following general formula:[M^((II)) _(1-x)M^((III)) _(x)(OH)₂]B·nH₂Oin which M^((II)) denotes a divalent metal ion, M^((III)) a trivalentmetal ion, B a mono- or polybasic organic or inorganic anion and n=0-10.There are natural and synthetic double-layer hydroxides in whichM^((II)) is a divalent ion, for example, magnesium, zinc, calcium, iron,cobalt, copper, cadmium, nickel and/or manganese and M^((III)) is atrivalent ion, for example, aluminum, iron, boron, manganese, bismuthand/or cerium.

A double-layer hydroxide that occurs in nature is hydrotalcite, which isderived from the mineral brucite and satisfies the following idealformula:[Mg₆Al₂(OH)₁₆]CO₃·nH₂O

Some magnesium ions in hydrotalcite are replaced by aluminum ions sothat the individual layer acquires a positive charge. This is balancedby carbonate anions that are situated in the interlayers together withwater of crystallization.

The double-layer hydroxide, however, can also be easily producedsynthetically by conversion of di- and trivalent metal salt solutions,for which DE-A-198 36 580 is referred to.

Magnesium oxide, hydroxide or carbonate, as well as dolomite, calciumcarbonate (for example, chalk) are considered as example for reactivefillers from the group of oxides, hydroxides or carbonates of alkalineearth metals. Either the natural mineral or synthetically producedproducts can be used for this purpose. Calcium carbonate is used withparticular preference, which during decomposition of polyvinyl chloridereacts with the formed hydrogen chloride and in this manner fulfills thedual function of an HCl scavenger and a processing auxiliary. The sameapplies for zinc carbonate. The corresponding oxides and hydroxides havethis dual function, since water is liberated during conversion of thesesubstances with hydrogen chloride, which interrupts combustion.

Surface modification of the active filler preferably occurs withamphiphilic aminoplastic-ether polymers. The aminoplastic central unitis preferably derived from monomers of the formula

Preferably R represents a lower alkyl group, especially a methyl orethyl group. The Z central unit is preferably derived from glycoluril.

The molar ratio between aminoplastic central unit Z and the group—[OCH₂—CH₂]_(n)—O— is preferably about 0.5 to 2, especially 0.5 to 1.7.

The molar ratio between substituents R and the aminoplastic central unitZ is preferably about 0.5 to 4, especially about 0.5 to 2.

The amphiphilic polymer or copolymer is preferably present in an amountof about 0.1 to 5, especially about 0.1 to 2 wt %. At amounts of morethan about 5 wt %, problems can occur during incorporation of thesurface-modified fillers in the polymer masses. An unduly high fractionof amphiphilic polymer in halogen-containing polymer masses reduces thethermal stability of PVC.

The object of the invention is also a method for production of thesurface modified in organic fillers described, characterized by the factthat

-   -   (a) a solution or a suspension of amphiphilic polymer or        copolymer is contacted with a reactive filler in the form of a        dry powder, a wet mass or a suspension, the solvent or        dispersant is removed and the obtained product optionally        ground; or    -   (b) the amphiphilic polymer or copolymer is contacted with the        reactive filler in the form of a melt; or    -   (c) the amphiphilic polymer or copolymer is ground dry with the        reactive filler.

The method according to the invention is preferably conducted so that(variant a) the amphiphilic polymer or copolymer is initially allowed toswell in an organic cosolvent; or (variant b) the melt of theamphiphilic polymer or copolymer is applied at a temperature between themelting point and 200° C.; or (variant c) grinding is carried out at atemperature between room temperature and 200° C.

An object of the invention is also the use of the surface modifiedinorganic active fillers just defined as additives to polymer masses,especially to halogen-containing polymer masses like polyvinyl chloride.

The surface modified fillers can be processed to a compound according tothe usual methods with the polymer masses. Commercial mixing units offerthemselves as compounding aggregates for this purpose, like single ortwin-screw kneaders, co-kneaders, internal mixers or a roll stand (PVC).The contents of surface-modified fillers can be added in an amount of0.1 to 70 wt % depending on the filler and the corresponding polymermatrix. Hydrotalcites are generally added to halogen-containing polymersbetween 0.1 and a maximum of 15 wt %.

The invention is explained nonrestrictively by the following examples.

For purposes of this application a translation of Example 2 from DE-A198 36 580 is incorporated, as follows:

Example 2

a) Synthesis of hydrotalcite in the carbonate form

In a 10 l reaction vessel 203 g MgCl₂×6 H₂O and afterwards 121 g AlCl₃×6H₂O are dissolved in 7 l demineralised water. Then the p H is adjustedto 10.5 by adding a 10% sodium carbonate solution. The reaction mixtureis heated to 80° C. and kept at this temperature for 24 h whilestirring. The solid matter is then separated from the liquid with asuction filter and the filter cake is washed three times with 1 literdemineralised water. The washed precipitate is then dried for 24 h at110° C. in a forced-air oven and milled with a pin beater mill to aparticle size of <63 μm.

The layer distance was determined by X-ray to be 0.7 nm.

b) hydrotalcite surface modified with sodium stearate (comparison)

250 g of the hydrotalcite obtained in example 2a are suspended in 5liters of demineralised water and then heated to 80° C. Then, 3 litersof an aqueous solution of sodium stearate containing 25 a sodiumstearate are added. The reaction mixture is stirred for 24 h at 80° C.and then filtered with a suction filter. The precipitate is washed threetime with 1 liter demineralised water each, dried in a forced-air ovenat 110° C. for 24 h and then milled to a particle size of <63 μm.

The layer distance was determined by x-ray diffraction to be 0.7 nm.i.e. there has not occurred any widening of the layer distance.

EXAMPLE 1

A hydrotalcite in carbonate form produced according to example 2(a) ofDE-A 198 36 580 was prepared as follows:

In a 10 l reaction vessel 203 g MgCl₂×6 H₂O and afterwards 121 gAlCl—3×6 H₂O are dissolved in 7 l demineralized water. Then the pH isadjusted to 10.5 by adding a 10% sodium carbonate solution. The reactionmixture is heated to 80° C. and kept at this temperature for 24 h whilestirring. The solid matter is then separated from the liquid with asuction filter and the filter cake is washed three times with 1 literdemineralised water. The washed precipitate is then dried for 24 h at110° C. in a forced-air oven and milled with a pin beater mill to aparticle size of <63 μm.

The layer distance was determined by X-ray to be 0.7 nm.

100 g of this hydrotalcite was coated with 0.5, 1.0 and 2.0 wt % of anamphiphilic copolymer of the aforementioned general formula in which forcompound A, Z=glycoluril, n=180, m=16, S=tristyrylaryl and for compoundB, Z=glycoluril, n=180, m=40, S=arylacryl.

Differential calorimetry studies (DSC) showed that the melting point ofthe two modifying agents lies at 49.5° C. Decomposition occurred attemperatures of about 120 to 180° C. Brown coloration appeared after 3hours at 180° C.

Coating of the reactive filler was conducted as follows.

Variant (a)

10% aqueous solutions of organic modifying agents A and B were appliedto 50 g wet hydrotalcite filter cake (water content about 35 wt %),dried at 150° C. for 2 to 3 hours in a drying cabinet, and ground.

Variant (b)

The organic modifying agents A and B were mixed in highly crushed formwith the hydrotalcite filter cake before or after drying, and ground.

Variant (c)

The organic modifying agents A and B were melted and mixed with thehydrotalcite before or after drying, and ground. The viscosity of themodifying agents is so limited at 60 to 80° C. that it can be addeddropwise.

Variant (d)

Hydrotalcite is mixed with water, and the organic modifying agents A andB are added under good agitation. The obtained slurry can be fed todrying, for example, by means of a spray dryer. The slurry can also befiltered and the filter residue fed to drying, for example, belt drying.

The method according to the invention can expediently be integrated in aprocess for production and processing of fillers.

The hydrotalcites modified according to variants (a) to (d) wereincorporated in known fashion dry in the soft PVC powder mixtures. ThePVC powder contains stabilizers (zinc stearate, Rhodiastab 50) andplasticizers (diisododecyl phthalate).

For comparison, an unmodified hydrotalcite from Kyowa Co. andhydrotalcites modified with amphiphilic copolymers A and B wereincorporated in soft PVC powder.

For the modification of the hydrotalcites a method was used as describedin example 2(b) of DE-A-198 36 580 as follows:

250 g of the hydrotalcite were suspended in 5 liters of demineralisedwater and then heated to 80° C. Then, 3 liters of an aqueous solution ofamphiphilic copolymers A or B containing 25 g amphiphilic copolymers Aor B were added. The reaction mixture was stirred for 24 h at 80° C. andthen filtered with a suction filter. The precipitate was washed threetimes with 1 liter demineralised water each, dried in a forced-air ovenat 110° C. for 24 h and then milled to a particle size of <63 μm.

For incorporating the hydrotalcite in the soft PVC powder, the fillerwas mixed with the soft PVC powder and plasticized in known fashion on amixing roll stand at 180° C. or in a kneader.

The results are shown in Table I.

TABLE I Properties of surface-modified hydrotalcites. Standard HT and HTand “Alcamizer 1” compound B compound A (Kyowa Co.) 2 wt % 1 wt % 2 wt %1 wt % VDE test 141 min −6.0% −2.8% −4.3% −2.8% Mathis furnace afterafter after after after discoloration 215 min 195 min 207 min 190 min207 min Flowability in — very good very good glass good good

The stabilizing effect of additives, especially hydrotalcites, ischecked in PVC generally with a VDE test according to DIN 53 581 PVC Aor VDE 0472 § 614 and the Mathis furnace test. In the VDE test, the timethat causes an irreversible chemical change from the effect of heat andis characterized by release of HCl is determined. The split-off HCl isdetermined by the color change of a universal indicator paper at pH 3.The percentage time deviation from the standard is evaluated.

In the Mathis furnace thermotest, PVC samples are exposed to a heat loadof different length, which is stipulated by the advance of a slide fromthe furnace. The color trend of the sample strip serves as relativegauge of the static temperature resistance.

The results of Table I show that no adverse effect on heat stabilitycould be observed from 1 wt % with compound A or B in the exampleaccording to the invention. It was found that a clearly antistaticfinishing of the active filler with compounds A and B is possible, whichsignificantly simplifies the flowability and consequently transport inthe installations and packing into sacks of the filler.

The effect of the antistatically finished active filler on theelectrical properties in PVC rolled sheet was investigated with anannular electrode. Measurement of the conductivity of the surfaceaccording to ASTM D257 is an evaluation criterion for antistaticadditives. The surface conductivity shows whether the material possesseshigh or limited conductivity, but is not necessarily a gauge ofelectrostatic power.

The results of the conductivity measurement on soft PVC rolled sheetsare summarized in Table II.

Experiment no. 1 contains the unmodified hydrotalcite Alcamizer 1 fromKyowa Co., experiment no. 2 contains hydrotalcite modified with compoundA (2 wt % modifying agent referred to HT).

TABLE II Specific Specific Resistance/Ω at resistance at resistance at100 V; 23.9° C. 40 V; 23.7° C.; 100 V; 23.9° C.; RH 15% RH 32.5% RH 15%Experiment 1 1.6 · 10⁹ 1.78 · 10¹² 6.3 · 10¹⁰ Experiment 2 1.3 · 10⁹1.98 · 10¹² 6.6 · 10¹⁰

The magnitude of the measured surface resistance lies in the range ofinsulating materials, i.e., the surface-modified hydrotalcite has noeffect in the employed amount on the electrical conductivity of the PVCrolled sheet. This is evaluated positively for application of soft PVCmixture as a cable sheathing (insulator).

The wetting effect in the aqueous phase was also investigated. Theunmodified hydrotalcite is not wetted by water in this case and floatson the water surface. The surface-modified hydrotalcites A and B arewell wetted by water and can be readily suspended. This property isimportant for mixing in polar media.

EXAMPLE 2

Surface modification of calcium carbonate.

100 g calcium carbonate was coated with 0.5 wt %, 1.0 wt %, 2.0 wt % and4.0 wt % compound A and compound B. Coating was conducted according tovariants (a) to (d).

EXAMPLE 3

Surface modification of magnesium hydroxide.

100 g magnesium hydroxide was coated with 0.5 wt %, 1.0 wt % and 4.0 wt% compound A and compound B. Coating was according to variants (a) to(d).

EXAMPLE 4

Surface modification of hydromagnesite.

100 g hydromagnesite was coated with 0.5 wt %, 1.0 wt %, 2.0 wt % and4.0 wt % compound A and compound B. Coating was conducted to variants(a) to (d).

1. A surface-modified inorganic surface filler comprising a reactiveinorganic filler modified by an amphiphilic aminoplastic-ether polymeror copolymer of the following structure:

in which: Z denotes the same or different aminoplastic central unitsbased on derivatives of melamine-formaldehyde, urea-formaldehyde,glycoluril or benzoguanimine; n=10 to 500; R denotes the group—[O—CH₂—CH₂]_(m)O—S in which m=5 to 500; and S represents a substitutedor unsubstituted alkyl, aryl, alkylaryl or aralkyl group.
 2. Thesurface-modified inorganic surface filler of claim 1 wherein thereactive inorganic filler comprises a double-layer hydroxide or anoxide, hydroxide or carbonate of an alkaline earth metal or zinc.
 3. Thesurface-modified inorganic surface filler of claim 2 wherein thedouble-layer hydroxide comprises hydrotalcite.
 4. The surface-modifiedinorganic surface filler of claim 1 wherein the aminoplastic centralunit Z is derived from monomers selected from the group consisting of

in which R represents a lower alkyl group.
 5. The surface-modifiedinorganic surface filler of claim 1 wherein the Z central unit isderived from glycoluril and wherein R represents an alkyl group with 5to 15 carbon atoms or an alkylaryl group with 5 to 15 carbon atoms inthe alkyl group.
 6. The surface-modified inorganic surface filler ofclaim 1 wherein the molar ratio between the aminoplastic central unit Zand the group —[OCH₂—CH₂]—O— is from about 0.5 to about
 2. 7. Thesurface-modified inorganic surface filler of claim 1 wherein the molarratio between the aminoplastic central unit Z and the group—[OCH₂—CH₂]—O— is from about 0.5 to about 1.7.
 8. The surface-modifiedinorganic surface filler of claim 1 wherein the molar ratio between thesubstituent R and the aminoplastic central unit Z is from about 0.5 toabout
 4. 9. The surface-modified inorganic surface filler of claim 1wherein the molar ratio between the substituent R and the aminoplasticcentral unit Z is from about 0.5 to about
 2. 10. The surface-modifiedinorganic surface filler of claim 1 wherein the amphiphilic polymer orcopolymer is present in an amount from about 0.1 to about 5 weightpercent.
 11. The surface-modified inorganic surface filler of claim 1wherein the amphiphilic polymer or copolymer is present in an amountfrom about 0.1 to about 2 weight percent.
 12. A surface modified polymercomprising the surface modified filler of claim 1 blended with apolymer.
 13. The polymer of claim 12 wherein the surface modified fillercomprises from about 0.1 to about 70 weight percent.
 14. A surfacemodified polymer comprising the surface modified filler of claim 1blended with a halogen-containing polymer.
 15. A method for theproduction of a surface-modified inorganic surface filler comprisingmixing a solution or suspension of an amphiphilic polymer or copolymerwith a reactive filler, wherein the filler is in the form of a drypowder, a wet mass or a suspension; removing the solvent or dispersantfrom the mixture; grinding the attained powder to form the filler,wherein the amphiphilic polymer or copolymer comprises the followingstructure

in which: Z denotes the same or different aminoplastic central unitsbased on melamine-formaldehyde or urea-formaldehyde derivatives; n=10 to500; R denotes the group —[O—CH₂—CH₂]_(m)O—S in which m=5 to 500 and Srepresents a substituted or unsubstituted alkyl, aryl, alkylaryl oraralkyl group.
 16. The method of claim 15 wherein the amphiphilicpolymer or copolymer is initially allowed to swell in a solvent.
 17. Amethod for the production of a modified inorganic surface fillercomprising blending an amphiphilic polymer or copolymer in the form of amelt with a reactive filler wherein the amphiphilic polymer or copolymercomprises the following structure:

in which: Z denotes the same or different aminoplastic central unitsbased on melamine-formaldehyde or urea-formaldehyde derivatives; n=10 to500; R denotes the group —[O—CH₂—CH₂]_(m)O—S in which in 5 to 500 and Srepresents a substituted or unsubstituted alkyl, aryl, alkylaryl oraralkyl group.
 18. The method of claim 17 wherein the melt of theamphiphilic polymer or copolymer is brought to a temperature between itsmelting point and 200° C.
 19. A method for the production of a modifiedinorganic surface filler comprising dry grinding an amphiphilic polymeror copolymer with a reactive filler wherein the amphiphilic polymer orcopolymer comprises

in which: Z denotes the same or different aminoplastic central unitsbased on melamine-formaldehyde or urea-formaldehyde derivatives; n=10 to500; R denotes the group —[O—CH₂—CH₂]_(m)O—S in which m=5 to 500 and Srepresents a substituted or unsubstituted alkyl, aryl, alkylaryl, oraralkyl group.
 20. The method of claim 19 wherein the amphiphilicpolymer or copolymer is ground with the reactive filler at a temperaturebetween room temperature and 200° C.